The present invention pertains to shingling of cut sheets and, more particularly, to an apparatus and method for shingling sheets immediately after cutoff and directly as the cut sheets exit the cutoff knife.
In the dry end conversion of a corrugated paperboard web, the continuously moving web, which may have already been longitudinally slit and/or scored, advances through a rotary cutoff knife where the web is cut crosswise into sheets of selected length. The cut sheets are conveyed into a stacking device where stacks of sheets are formed and transferred away for further processing. In a modern corrugator dry end, the cutoff knife comprises a pair of counterrotating rotary knives with helical cutting blades. Variable speed drive systems are utilized to control blade speed to cut sheets of widely varying lengths from the web which may be running at the speeds in excess of 1,000 feet per minute.
In order to slow the cut sheets for stacking without damage and to shorten the length of the conveyor system delivering sheets to the stacker, cut sheets are typically formed into a shingle at some point downstream from the cutoff knife, thereby allowing the stream of sheets to enter the stacker at a speed substantially below web line speed. Furthermore, to enhance sheet handling, cut sheets are typically accelerated slightly after cutoff (e.g. to about 110% of web line speed) to form a slight gap between successive sheets. However, this adds to the total length of the system between the cutoff knife and the stacker.